This invention relates to homopolar generators and more particularly to such generators in which the stator field coil is connected in series with the brushes to limit initial current rise and to prolong output current pulse duration.
Homopolar generators have been successfully designed for providing short duration pulses having a peak current level in excess of a million amperes DC. Such generators generally include a cylindrical rotor of either a drum or disc configuration, mounted on frame, and rotated about an axis through the center of the cylinder. A field coil encircling the rotor and connected to an external current supply provides an applied field excitation passing through the rotor. The applied field excitation is usually confined and directed by a ferromagnetic yoke surrounding the field coil and all, or a portion of, the rotor. When the rotor is spinning, the free electrons within the rotor experience an electromotive force resulting from their interaction with the applied field excitation. Brushes, positioned inside the field coil or between two halves of the field coil, are then lowered onto the spinning rotor to allow an electrical current to flow under the influence of such electromotive force through return conductors to an external circuit, and then back onto the rotor through additional brushes at a different location. During the discharge, the interaction of the discharge current in the applied field excitation creates a force which decelerates the rotor until its rotation stops and the discharge therefore ends. It has been found, that extremely high current pulses may be obtained after using a relatively low power conventional prime mover or a conventional low voltage, low amperage power source to store initial energy in the rotor by gradually motoring the rotor up to the desired rotational speed.
Homopolar generators have been found to be useful in electromagnetic projectile launching systems wherein a high current power source comprising the series connection of a homopolar generator and an inductive energy storage coil is connected to a pair of conductive projectile launching rails. A sliding conductive armature is positioned between the rails such that when current is switched from the high current power source to the rails, current flow in the rails and through the armature places an electromagnetic force on the armature which propels it along the rails. Electromagnetic launching systems have been constructed which use a compensated winding, shunt field excited homopolar generator which has very low impedance in series with an air core toroidal inductor to supply current to a parallel rail launcher. Where a large payload, such as a manned aircraft, is to be launched, it is desired to have a gradual buildup of acceleration which has a duration of several seconds. For such an application, the series connection of an air core toroidal inductor and a homopolar generator becomes unwieldy because of the size of the inductor required to limit the initial current rise and to prolong the pulse duration. This invention surmounts this problem by combining the function of the toroidal inductor and the homopolar generator into a single unit. The field of the coil is thereby used to provide the field of the homopolar generator. This also minimizes the external field power supply requirements. By proper design of the time constant of the series field coil, it is possible to provide a slow buildup in the field flux and armature current, thus providing a controlled current buildup and an improved ratio of effective to peak current. By providing a permanent magnet or auxiliary pilot winding to augment initial residual flux, it will be possible to minimize or eliminate the need for an external power supply.
This invention is a self-excited, high current, DC pulse generator that will require a minimum of external supporting equipment. A pulse generator constructed in accordance with this invention comprises: a stator member; a rotor concentrically positioned within the stator member and mounted for relative rotation therewith; a main stator winding including two winding sections which encircle the rotor and are helically wound and coaxial with the rotor, wherein the winding sections are electrically connected in series with each other; a pair of brushes disposed in sliding contact with the rotor, mounted on opposite sides of the main stator winding, and electrically connected to opposite ends of the main stator windings; a third brush disposed in sliding electrical contact with the rotor and mounted at an intermediate position on the rotor between the first pair of brushes; and means for rotating the rotor. An external load can be connected between the third brush and the common point of the two winding sections.
This invention also encompasses a dual rotor electric pulse generator comprising: a stator member; first and second rotors positioned within the stator member and mounted for rotation in opposite directions about a common axis relative to the stator member; a main stator winding being helically wound and coaxial with the rotors; first and second brushes disposed in sliding electrical contact with the first rotor and mounted at axially displaced locations along the first rotor, wherein the second brush is connected to one end of the main stator winding; third and fourth brushes disposed in sliding electric contact with the second rotor and mounted at axially displaced locations along the second rotor, wherein the third brush is connected to the other end of the main stator winding; and means for rotating the first and second rotors. In a dual rotating drum generator in accordance with this invention, an external load is connected between the first and fourth brushes. The rotors of both the single rotor and the dual rotor generators can be rotated by way of connection to an external driving means, or by being motored up by connection to an external power source while the rotors are in the presence of a magnetic field.